It is often necessary to dig trenches to bury conduits for electrical power hook-ups, or for burying similar cable-like conduits such as television antenna cables, telephone cables, water supply pipes, and lawn sprinkling system pipes. A conventional trenching apparatus includes a boom assembly mounted on and extending rearwardly from a relatively large tractor or back hoe, frequently of the track type.
Where the area in which the trench is to be provided has already been landscaped and especially when only a relatively narrow trench of reduced depth is required, conventional trenching machines are excessively large and cause a much greater amount of destruction to existing landscaping than is necessary. Relatively large vehicles such as back holes and the like do not readily adapt to certain types of terrains such as steeply sloped or terraced areas. Moreover, the hourly cost of operating large equipment is often not just justified when only a relatively narrow ditch having a reduced depth is to be dug thereby.
There is an increasing demand, therefore, for a portable, walk behind trencher machine. Such a machine typically includes a self-propelled and wheeled frame. A power source such as a small pull/start internal combustion engine is typically mounted on the frame for driving the trenching tool i.e., an endless digging chain designed to dig a relatively narrow trench for use in situations such as those mentioned above. The digging chain is commonly mounted on a boom which is movable to different elevational positions.
In larger trencher machines, the controls for operating the trencher are typically located in a cab region of the machine away from the digging chain assembly. In contrast, and primarily because of the vast differences in their sizes, portable or walk behind trenchers typically have the controls for the machine in proximity to the engine and trenching tool on the machine. Such controls typically include one or more ground drive controls for regulating direction and speed of the trenching machine, a digging chain control for regulating operation of the digging chain assembly, and a boom lift controller for regulating the elevation of the boom relative to the frame and the digging chain assembly carried thereby thus regulating the depth of the trench being dug by the trenching machine.
On conventional trenchers, the ground drive control and digging chain control are complicated by each having a control switch or monitor associated therewith and responsive to movement thereof. Conventional trenchers further include an electrical system which includes and is responsive to the switches or monitors associated with the control levers. Inexperience with the machine and/or the routineness of trenching operations, can lead to careless mistakes by the operator and/or persons in the area of the trencher. Therefore, unless both switches detect or monitor that the respective control member is in a neutral position, the electrical system will inhibit starting of the power system.
As will be appreciated, the control levers associated with conventional trenchers are often shifted to change trencher operations. That is, the ground drive control is often shifted between forward and reverse through a neutral position or condition. Likewise, during trencher operations, the digging chain control lever is often shifted from its disengaged condition to effect operation of the digging chain. The continuous shifting of the control levers during trencher operations applies a relatively high cyclic loading on the switches or monitors of the electrical system. Failure of one or both of the switches results in costly downtime of the trencher to effect repairs thereof. Moreover, failure of either or both switches during a starting procedure can result in inadvertent starting of the trench yielding undesirable conditions.
Thus, there is a need and a desire for a simplified and reliable control system which permits starting of a walk behind trencher machine only after certain starting criteria are satisfied.